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For a lens system with f₁ = 5 cm and f₂ = 2 cm, calculate the focal length of the combined system.

1. f = 2 cm
2. f = 5 cm
3. f = 1 cm
4. f = 3 cm

Correct answer: f = 1 cm

Solution

The focal length of a combined lens system is given by 1/f = 1/f₁ + 1/f₂. Substituting f₁ = 5 cm and f₂ = 2 cm, we get 1/f = 1/5 + 1/2 = 7/10. Thus, f = 10/7 ≈ 1 cm.

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